linux-kernel - [PATCH 5.4 101/165] psi: Fix a division error in psi poll()

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Message-Id: <20200111094930.155151632@linuxfoundation.org>
Date:   Sat, 11 Jan 2020 10:50:20 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Jingfeng Xie <xiejingfeng@...ux.alibaba.com>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 5.4 101/165] psi: Fix a division error in psi poll()

From: Johannes Weiner <hannes@...xchg.org>

[ Upstream commit c3466952ca1514158d7c16c9cfc48c27d5c5dc0f ]

The psi window size is a u64 an can be up to 10 seconds right now,
which exceeds the lower 32 bits of the variable. We currently use
div_u64 for it, which is meant only for 32-bit divisors. The result is
garbage pressure sampling values and even potential div0 crashes.

Use div64_u64.

Signed-off-by: Johannes Weiner <hannes@...xchg.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>
Cc: Jingfeng Xie <xiejingfeng@...ux.alibaba.com>
Link: https://lkml.kernel.org/r/20191203183524.41378-3-hannes@cmpxchg.org
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 kernel/sched/psi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 970db4686dd4..ce8f6748678a 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -482,7 +482,7 @@ static u64 window_update(struct psi_window *win, u64 now, u64 value)
 		u32 remaining;
 
 		remaining = win->size - elapsed;
-		growth += div_u64(win->prev_growth * remaining, win->size);
+		growth += div64_u64(win->prev_growth * remaining, win->size);
 	}
 
 	return growth;
-- 
2.20.1